The invention relates to a method of regulating the heat of an internal combustion engine for vehicles in accordance with the features of the precharacterizing clause of claim 1.
The management of the heat of an internal combustion engine and of a vehicle, that is to say the cooling and heating of units and devices to an optimum operating temperature, is of decisive importance for the efficiency and therefore for the vehicle system, especially with regard to economy, functioning, service life and comfort. It is therefore desirable for the devices and units, especially the internal combustion engine of the vehicle, to reach their optimum operating temperature as quickly as possible and maintain it as far as possible during the entire operation.
EP 0 499 071 A1 discloses a cooling system for a vehicle with an internal combustion engine. The cooling system comprises several circuits with associated heat exchangers. The temperatures of different cooling media are measured and are processed in a central evaluation device to form output signals by means of which electrically controllable devices, such as controlled-speed pumps, controlled-speed fans, electrically controllable valves and a louvre shutter arranged in the air flow path can be driven. For all the cooling circuits, the heat-exchanger capacity or the rotational speed of the fan is always directed towards the highest requirement of one of the cooling circuits. The central management of the heat achieves the situation where little drive energy has to be applied for pumps and fans for the cooling and heating of the system and not too much energy is extracted from the system. As a result, the required operating temperatures are reached quickly upon starting.
However, there is the difficulty to intervene in good time in the regulation of the heat, since the cooling medium temperatures used for the control are only established at a higher or lower temperature level relatively late after the actual accumulation of heat. In addition, the registration itself of the temperature is subject to considerable delays.
DE 37 38 412 A1 discloses a method for regulating the heat of an internal combustion engine, in which the delivery capacity of the electrical pumps is controlled not only as a function of the cooling-medium temperature but as a function of at least one further characteristic operating variable. For this purpose, an electronic switching device receives, as input signals, the operating temperature of the internal combustion engine, the air temperature in the immediate environment of the internal combustion engine, the ambient temperature which can be measured at a greater distance from the internal combustion engine, the temperature of engine parts and the rotational speed of the internal combustion engine, and information about the speed of travel of the vehicle. The electronic switching device processes the input signals to form output signals and initially outputs an output signal to the electric pump. Further output signals are output to the valves, if appropriate, and to an actuating device which operates an adjustable louvre shutter arranged in front of a heat exchanger used as a cooler, and finally to fan motors associated with heat exchangers.
EP 0 084 378 A1 discloses a control device for a cooling system of an internal combustion engine in which the input variables are evaluated by means of a microprocessor. The input variables used are the cooling-water temperature, the speed of the vehicle and the ambient temperature.
DE 38 10 174 A1 shows a device for regulating the cooling-medium temperature of an internal combustion engine, a regulating device or evaluation device receiving, as input signals, the load and the rotational speed of the internal combustion engine, in addition to the cooling-water temperature. The load on the internal combustion engine can be determined indirectly by measuring the intake-pipe vacuum of a mixture-compressing internal combustion engine, or by measuring the position of the control rod of an injection pump of an air-compressing internal combustion engine.
Furthermore, DE 41 09 498 discloses a method of regulating the temperature of an internal combustion engine in which a control device processes, as input signals, the following operating parameters: the temperature of the internal combustion engine, the intake temperature, the rotational speed of the internal combustion engine, the speed of the vehicle, the load on the internal combustion engine, the operating state of the air-conditioning system, the heating of the motor vehicle, the time, the diagnostic information, an output signal from a knock control device and the temperature of the cooling water.
In addition, DE 44 26 494 A1 discloses a device for monitoring the cooling system in an internal combustion engine. The serviceability of the cooling system is monitored by using a microprocessor, by the variation of a temperature signal being evaluated and detected temperature changes per unit time being compared with plausible values. The devaluation is not used to regulate the cooling system, but only to monitor it and to be able to detect misfunctions surely and reliably.
Finally, U.S. Pat. No. 4,768,484, which forms the generic type, discloses a method of regulating a thermal device in which, using a microprocessor, signals from temperature sensors are fed to an electronic evaluation unit having a microprocessor. However, the possibilities of (rapid) action on the development of heat are limited.
The invention is based on the object of proposing a method in which interventions in the heat regulation of the internal combustion engine can be made more rapidly and more directly.
According to the invention, this object is achieved by the features of claim 1. In the method according to the invention, in addition to the temperatures of the cooling or heating media, critical component temperatures and/or characteristic output values of the internal combustion engine are registered and taken into account in the regulation. Since the critical components react more directly to an increased accumulation of heat and their temperature changes considerably earlier, before the cooling-medium temperature reacts with a delay as a result of the transfer of heat, interventions in the heat regulation can be made rapidly. This is accelerated by the method according to the invention, by not only the component temperatures and/or characteristic output values as such, but changes per unit time being taken into account in the regulation. The trend of the temperature variation gives an important indication early on as to whether more intensive or less intensive cooling must be carried out.
A critical component which is suitable for this is the cylinder head of an internal combustion engine, specifically the region between outlet valves, the so-called web zone. Since this region is exposed to the hot exhaust gases, it is particularly threatened by high temperatures and frequent temperature changes. Because of its low mass and its position, it reacts very quickly to changes in the heat loading, so that its temperature is very characteristic of the accumulation of heat in the internal combustion engine.
According to the method of the invention, it is further proposed to register characteristic output values of the internal combustion engine which are specific to the heat behaviour, for example, expediently, the amount of fuel introduced into a combustion chamber per unit time or per working cycle. In this way it is possible to obtain a characteristic variable for the regulation before the actual accumulation of heat takes place or a critical component has reached the corresponding temperature. In principle, it is possible to register the temperatures and characteristic values of all the cylinders of an internal combustion engine. As a rule, however, it will be sufficient if only the values of the most critical cylinder or some cylinders are registered.
By means of the method according to the invention and its refinements, it is possible for the optimum operating temperatures to be reached particularly quickly in the starting phase of an internal combustion engine for vehicles if, as the temperature rises or the accumulation of heat builds up, from among the devices, first the pumps are put into operation and regulated, then the thermostats, then the louvre shutter and finally the fan.
The achievement of all these measures is that the combustion chamber is heated up very quickly after the start, with the result that the cylinder charging, both in spark-ignition and in diesel engines, burns better and therefore lower hydrocarbon emissions result. In addition, self-ignition in diesel engines is improved, as a result of which, even after a very short warm-up time, a more uniform and very quiet running with a considerably reduced emission of noise is reached. Because of low heat losses via the combustion-chamber wall, the idling rate, which is usually increased during starting, can be reduced considerably earlier, and the period during which the rate is increased can be shortened considerably. As a result, the thermal efficiency during these operating states is improved, and the fuel consumption is reduced.
Finally, the exhaust-gas temperatures rise very rapidly, as a result of which a catalytic converter responds more quickly, and the response behaviour of a turbocharger is improved. Since the regulation of the heat responds very quickly when the temperatures change or the accumulation of heat changes, the components of the internal combustion engine are better protected against thermal overloading. In addition, the lubricating oil is brought quickly to an optimum temperature, so that it develops its full functional capacity very soon, without its ageing being threatened by overloading.